The determination of the location and strength of shockwaves and vortices is fundamental to understanding the flow around an aircraft. These features are strong enough to affect the environment that the vehicle inhabits. For example, they can cause drag and/or produce undesirable noise. The researcher must be able to predict and mitigate the effects of these flow features.
The best method for discovering new physics and/or validating computational models is by making measurements on a full-scale aircraft in flight. Importantly, a technique that can visualize and measure the strength of flow features would be highly advantageous to researchers.
An early method for airborne Schlieren makes use of the sun's edge as viewed through a telescope. The aircraft was observed and recorded through a telescope on the ground pointed at the sun as the aircraft passed through the field of view. The aircraft's shockwaves would distort the edge of the sun. High speed imaging of the fly-by was processed to extract the distorted edge and create a streak image of the airplane and its shockwaves. This method has the advantage of having the imaging system on the ground, thus reducing the cost by eliminating the observer aircraft.
The imagery of the shockwaves from this earlier method was unfortunately limited by the narrow field of view defined by the sun. Further, ground-based systems, using the sun as a light source, have produced good results but because of the distance involved did not have the desired spatial resolution to resolve small-scale shock structures near the aircraft. Also, the solution from this method does not currently have a theory or method by which the density gradient can be derived and thereby measured.
Accordingly, in light of the shortcomings of the previous solutions, there clearly exists a need for a modern version of the airborne Schlieren method to capture images of shockwaves created by supersonic airplanes that includes increased field of view and resolution enabling more precise calculations.